Seedling A ncttomy of Certain Sympetalae . II. 317 
species of Chrysanthemum the arrangement of the median strand begins 
in the long cotyledonary tube, and is soon completed. 
very short (2-3 cm. long) and 
slender ; the vascular strands throughout are correspondingly small, and the 
transition is exactly similar to that in Chrysanthemum Parthenium , the root 
being diarch in structure. 
Tribe VIII. Senecioneae. 
Senecio clivorum, Maxim. In all the seedlings, which varied in length 
from 7-10 cm., the hypocotyl was comparatively short (less than 1 cm.), 
and the seed-leaves, which were spatulate in shape and were furnished with 
long petioles, were distinctly unequal in size. 
The venation of the cotyledons is not peculiar. The numerous bundles 
present in the leaf-blade fuse in various ways to give rise to a large midrib and 
two small laterals, all of which run down the petiole and enter the hypocotyl 
almost unchanged. In the upper part of the latter each midrib bundle under- 
goes modification : the phloem bifurcates, and the two halves travel laterally, 
while in the wood portion the protoxylem begins to take up an exarch 
position. The intercotyledonary strands produced by the fusion of the 
laterals in pairs pass to the centre of the hypocotyl, and after a longer or 
shorter distance has been traversed, they gradually die out. The phloem 
groups having previously assumed a lateral position and fused in pairs, the 
midrib xylem masses meet at the centre, and a typical diarch root is pro- 
duced. Altogether the transition is like that in Charieis heterophylla. 
In the region of the root-tip, after the pith has completely disappeared, 
there is often a return to an almost tetrarch condition : this is brought 
about by the enlargement of the xylem in the intercotyledonary plane, 
and the subsequent more or less complete division of the phloem masses. 
Tribe IX. Calenduleae. 
Silybium Marianum , Gaertn. Seedlings 8-10 cm. long, and rather 
massive. 
The course of the vascular strands in the cotyledon is the same as in 
Silphium perfoliatum (p. 308). The bundles formed by the fusion of the 
four laterals on either side of the midrib are smaller than the latter, and 
their protoxylem groups never become exarch. With the decrease in size 
of the hypocotyl in passing downwards, the intercotyledonary strands travel 
centrewards, then dwindling in size, they move laterally in a clockwise 
manner (as seen from above), and fuse with the flattened midrib. There is 
no real tetrarch arrangement, but at the base of the hypocotyl the midrib 
xylem groups, each of which by this time has a definite protoxylem, meet 
